Avoid 2nd degree polynomial regexp for sanitizing content type

This can lead ot ReDos on Ruby 3.1 and older.

lib/rack/utf8_sanitizer.rb

@@ -118,9 +118,13 @@ def sanitize_rack_input(env)
  # https://github.com/rack/rack/blob/master/lib/rack/request.rb#L42
  # Logic borrowed from Rack::Request#media_type,#media_type_params,#content_charset
  # Ignoring charset in content type.
- content_type = env['CONTENT_TYPE']
- content_type &&= content_type.split(/\s*[;,]\s*/, 2).first
- content_type &&= content_type.downcase
+ if content_type = env['CONTENT_TYPE']
+ content_type = content_type.split(/[;,]/, 2).first
+ if content_type
+ content_type.strip!
+ content_type.downcase!
+ end
+ end
  return unless @sanitizable_content_types.any? {|type| content_type == type }
  uri_encoded = URI_ENCODED_CONTENT_TYPES.any? {|type| content_type == type}